As the dangers and environmental impact of traditional coal, oil, gas and nuclear power generation become better understood and appreciated, there is an increasing desire for alternative forms of generating power. In recent years, one of the more successful alternative methods of generating energy has been wind power. There are many different known arrangements for generating wind power, but most rely on the principle of providing a turbine having blades arranged to turn as a result of the force of the wind and to thereby generate energy.
The efficiency with which such wind-based electricity generation occurs depends upon the efficiency with which the kinetic energy of the wind can be converted into electrical energy which, in turn, depends upon the efficiency with which the blades can rotate about their axis of rotation.
Due to the manner in which wind turbines operate, the blades which rotate under the influence of the wind are often orientated to rotate vertically with respect to the ground. Therefore, for each up-stroke it is necessary to lift the blade against the force of gravity.
Furthermore, one of the known problems experienced during wind generation is that the blade arrangement (or the portion undergoing rotation due to the wind) is subjected to significantly varying forces as the speed of the wind changes. It is therefore known to vary the moment of inertia of the blade arrangement by varying a weight arrangement about an axis of rotation. Such an arrangement is, for example, disclosed in WO 2004/011801. However, such known arrangements vary the moment of inertia symmetrically about the axis of rotation. Furthermore, the means proposed for varying the moment of inertia rely on relatively expensive and friction-inducing arrangements.
Current turbines require a minimum wind speed to operate, provide a near linear increase in output power with an increase in wind speed, and have a maximum rated output power which, when achieved, does not increase with wind speed. Turbines produce the maximum output power as wind speed further increases up to a point when, at a predetermined wind speed, the turbine is shut down to protect it from damage. A problem of the current turbines is that the range of wind speeds at which the turbine can produce power is limited.